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醛与醇/胺的氧化C-O/C-N偶联反应和机理研究
郭亚菲
学位类型博士
导师张锁江
2016-07
学位授予单位中国科学院研究生院
学位授予地点北京
学位专业化学工程
关键词醛的氧化官能化 酯和酰胺 协同催化 自由基反应
摘要

羧酸衍生物——酯和酰胺是重要的结构,对其合成方法的研究具有重要意义。传统的合成酯和酰胺的方法主要是通过羧酸及其活性衍生物与亲核试剂醇或胺发生酯化或酰胺化反应得到。通常需要将羧酸转化为活性衍生物,如卤代羧酸或酸酐等,不属于原子经济性反应。新的合成方法不断出现,其中通过醛与醇或胺在氧化剂存在下的一步氧化酯化反应(C-O交叉偶联)或氧化酰胺化反应(C-N交叉偶联)是一种有效地替代方法,由于其绿色和高效性而得到了较多关注。报道的方法也存在一些问题,如:采用的催化剂价格昂贵,需要高的醇醛比高等,另外一个重要的问题是缺乏深入的机理研究,不能为反应指明有效的改进方法。基于以上现状,本论文的研究开展了非贵金属钴催化的氧化酯化和氧化酰胺化反应,以及在免金属条件下离子型氧化剂用于氧化酯化反应,并对反应机理进行了研究。 (1)本论文开发了首例均相钴催化的醛的氧化酯化反应体系。该体系采用TBHP为氧化剂,CoI2做催化剂,添加助剂AlCl3以提高酯的选择性。该体系具有以下实用特性:无溶剂、低醇醛比、催化剂和助剂时是商化的廉价试剂。体系对芳香醛的位阻效应和电子效应不敏感,而且脂肪醛和杂环醛也都适用。利用UV-Vis分光光度计和XPS等对催化剂与氧化剂的作用过程进行研究,发现金属钴和配体碘在催化反应中价态均发生了变化,并对TBHP的分解产生影响。对不同碘化物的动力学对比分析发现金属钴和碘在催化过程中起到了协同的作用。原位生成的次碘酸根(IO-/IO2-)主要来自于I3-向IO3- 转化的过程,并协助氧中心自由基在关键的从半缩醛夺氢的反应中效率更高。 (2)以叔丁基过氧化氢的水溶液(T-HYDRO)为氧化剂,以CoI2为催化剂,实现了温和条件下的醛和胺类盐酸盐的高效氧化酰胺化反应,所采用的试剂廉价且简单易得。芳香醛和杂环醛均适用于该体系,提高氧化剂的量,醛的前驱体醇也适用于该反应。在反应中,以无水的氧化剂反应几乎不能生成产物,进行了重氧水同位素示踪实验,产物中有大量的18O标记的酰胺,可知水参与了反应,在催化条件下存在半缩胺中间体与亚胺的脱水/水合平衡反应。另外机理实验研究了反应过程中实际的夺氢试剂是原位生成的氧中心自由基t-BuO ?/t-BuOO?,而不是由碘离子转化成的高价碘如 IO-/IO2-/IO3-。 (3)免金属催化剂下实现氧化酯化反应由于其更强的绿色性,是更具吸引力的目标。而通过自由基机理实现氧化酯化反应由于可能出现的副反应多,是存在困难的。鉴于过硫酸根类氧化剂释放的SRA常用于不同的氧化反应中,本文通过阳离子的设计和调节,实现了对过硫酸根类氧化剂的氧化能力的调节和控制,最终实现了免催化剂条件下,过硫酸根类离子型氧化剂参与的醛的氧化酯化反应。反应在空气下操作,条件较温和,具有强实用性。通过自由基捕获实验等多种方式研究了反应机理,并对阴阳离子间作用对各步反应的影响进行了分析。发现反应经历了硫酸甲酯盐关键中间体,而阳离子对该中间体的形成动力学有明显影响。

其他摘要

The significance of carboxylic esters and amides has forced scientists to develop efficient methods for their preparation. Esters and amides are generally prepared via the reaction of carboxylic acid or activated acid derivatives such as acid anhydrides and acyl chlorides with alcohols or amines, which are not environment friendly methodology. Direct oxidative esterification (oxidative C-O cross coupling) or amidation (oxidative C-N cross coupling) of aldehydes with alcohols or amines are conceptually and economically attractive approaches and have received increasing attention. However, there are still problems in the developed system, for instance, the expensive noble metal catalyst and the demanding for excessive reagent. More importantly, there are few mechanistic studies on the oxidative coupling reactions, making it hard to understand the factors that control the efficiency. Accordingly, this thesis develops non-precious cobalt catalyst for efficient direct oxidative coupling of aldehydes with alcohols or amines. In addition, metal free system for oxidative esterification of aromatic aldehydes, which takes advantages of ionic oxidants, are developed. Whats more, detailed mechanism studies are presented. (1) The first homogeneous inexpensive cobalt catalyst system for oxidative esterification of aldehydes is disclosed. Where TBHP is used as oxidant and CoI2 as catalyst. AlCl3 is necessary additive to improve the selectivity of esters. And, the methods exhibit highly favorable practical characteristics: solvent free system, rather low alcohol/aldehyde ratio and the catalyst components are inexpensive and commercially available reagents. The methods are compatible with substrates bearing a variety of functional groups, including electron-poor or rich aromatic aldehydes, as well as aliphatic and heterocyclic aldehydes. Mechanism studies provide extensive insights into the cobalt mediated decomposition of TBHP in the presence of iodide ion. Investigations attribute the high efficiency to a cooperative effect between the iodide chelating ligand and cobalt ion on the catalytic cycle. The in situ generated hypoiodites (IO-/IO2-) mainly from conversion of I3- to IO3- accounts for a cooperative effect with the oxygen centered radical species to make the hydrogen abstraction from hemiacetal intermediates more selective, thereby offering the high efficiency. (2) A cobalt and iodide co-catalyzed oxidative amidation of alcohols/aldehydes with amines is developed. The straightforward process occurrs under mild and clean reaction conditions, using T-HYDRO as the terminal oxidant and makes use of readily available starting materials. The oxidative coupling of aromatic and heterocyclic aldehydes or alcohols with amines give the corresponding amides compounds in good to excellent yields. Investigation into the reaction mechanism also find the significant influence of water on the reaction and therefore disclose potential transiency of hemiaminal and an important role of its regeneration from hydration of imines under catalysis. Mechanistic studies indicats that the in situ generated t-BuO ?/t-BuOO? rather than that iodine related IO-/IO2-/IO3- is the active hydrogen abstraction species in such catalytic process. (3) Metal-free reactions are green approach es for scientists to achieve. And the oxidative esterification of aldehydes with alcohols through radical mechanism is problematic because the existence of various side reactions. A mild, convenient and practical oxidative esterification of various aromatic aldehydes by sulfate radical redox system are presented. The reaction pathways, especially the roles of various (doubly) ionic H-bonding toward S2O82- on the reaction efficiency, are fully discussed. The transiency of MeOSO3- is disclosed, which is generated from esterification between HSO4- and MeOH, a rate-limiting step in the oxidative esterification process. 

语种中文
文献类型学位论文
条目标识符http://ir.ipe.ac.cn/handle/122111/22884
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郭亚菲. 醛与醇/胺的氧化C-O/C-N偶联反应和机理研究[D]. 北京. 中国科学院研究生院,2016.
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